Cannot verify server identity keeps popping up on my phone. I cat do anything unless I constantly hit cancel. Please Help!!

What happens when you click the "Details" on the error popup message (See the Pic below)

Best would be to Delete and Add the email account that is creating the issue.

You may also try changing SSL settings

Settings > Password & Accounts > [Select the Mail account} > [Tape on Account with the email ID} > Advanced > SSL Settings > [Disable]

Click <Account (in Blue)

Click on DONE (in Blue) when exiting in the previous screen